docs: def _read_cache_from_file(self):
          """Read the contents of the cache from a file on disk."""
          cache = {}
          try:
              with(open(self._cache_file_name, 'r')) as fp:
                  contents = fp.read()
                  cache = simplejson.loads(contents)
          except (IOError, JSONDecodeError):
              # The file could not be read. This is not a problem if the file does not exist.
              pass
  
          return cache